This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2000-071968, filed Mar. 15, 2000.
The present invention relates to a method and apparatus for fabricating a substrate of, e.g., a semiconductor device or a liquid crystal display and, more particularly, to a substrate processing method and substrate processing apparatus using a liquid agent.
A semiconductor device or a liquid crystal display device is given desired functions by performing various processes on a substrate and finally forming fine patterns. To fabricate such a substrate, not only dry processes using gases but also wet processes using liquid agents are extensively used. For example, a wet process is used in a development step of forming a photosensitive resin pattern used in the fabrication of a fine pattern.
A method of forming a photosensitive resin pattern (resist) by using a wet process will be described below. A film to be processed formed on a silicon or quartz substrate is first coated with a photosensitive resin, and a portion of this photosensitive resin in a desired region is exposed to light by using an exposure mask.
Subsequently, a developer, e.g., an organic solvent or alkaline aqueous solution is used to remove an exposed portion, in the case of a positive resist, or an unexposed portion, in the case of a negative resist, thereby forming a photosensitive resin pattern. This step is called a development step.
A wet process is also used to fabricate a chromium film of a chromium mask for exposure. In this wet process, after a chromium film is formed on a quartz substrate, a photosensitive resin pattern is formed. A portion of the chromium film uncovered with this photosensitive resin pattern is isotropically wet-etched by using a ceric nitrate ammonium solution or the like.
Also, a mixed liquid agent of sulfuric acid and hydrogen peroxide is used to remove unnecessary organic substances sticking to the substrate before fabrication, and to remove the photosensitive resin pattern remaining after the etching process. Native oxide formed when atmospheric oxygen reacts with a silicon substrate is also removed using NH4F or dilute HF as a liquid agent, since this oxide prevents uniform fabrication. Furthermore, an Au plating solution is used to form a gold film on a silicon wafer.
Conventionally, a developer is supplied by using a nozzle having holes for supplying the developer from above a substrate to be processed. That is, the developer is supplied while a wafer is rotated, so that the supplied developer is spread by the centrifugal force. This method is disclosed in, e.g., Jpn. Pat. Appln. KOKAI Publication No. 5-13320. In this method, the developer is continuously supplied to a portion immediately below the developer supply holes. However, the developer spread by the centrifugal force dissolves resist while spreading on the wafer. Therefore an alkaline component in the developer is consumed and the alkali concentration lowers in a peripheral portion. As a consequence, a CD (critical dimension)/pattern size difference is produced between the portion just below the developer supply holes and the portion away from the developer supply holes on the surface of the substrate to be processed.
From the foregoing, it is desired to supply a developer as a liquid agent film onto a substrate to be processed. However, it is not easy to supply a liquid agent in the form of a film from an upper side of a substrate to be processed. That is, when a liquid agent film is placed on a substrate to be processed, the substrate repels this liquid agent if the contact angle between the substrate and the liquid agent is too large. To prevent this repellent of the liquid agent, it is necessary to supply more amount of liquid agent than the one needed for the processing. Consequently, a large amount of liquid agent is wasted.
In another method of forming a liquid agent film, a liquid agent film holding member is set above a substrate to be processed, and a liquid agent film is formed on the lower surface of this liquid agent film holding member. If, for example, the thickness of a developer film becomes a predetermined value or larger, a liquid agent consisting of this developer unfortunately falls as droplets. To prevent the formation of droplets, the thickness of the developer film must be decreased. As a consequence, enough amount of liquid agent for development can not be obtained.
To solve this problem, it is possible to set a substrate to be processed with its surface to be processed facing down, and place a liquid agent below the substrate. However, the conventionally proposed method is to perform dip development, in which a liquid agent such as a developer is stored in a liquid agent reservoir (e.g., disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101467). That is, the method requires a large amount of liquid agent.
Also, in this conventionally proposed method, a substrate to be processed is set parallel to the surface of a liquid agent, and is brought into contact with the liquid agent by lowering the substrate or raising the liquid agent reservoir. When this method is executed, a bubble enters between the substrate and the liquid agent and produces a defect or, even if it does not produce such a defect, produces variations in critical dimensions/pattern size. This bubble is formed because the entire surfaces of the liquid agent and the substrate are not brought into contact with each other at once.
One cause of the formation of a bubble is that air is surrounded with the liquid agent and the substrate because the time at which the liquid agent and the substrate come into contact with each other differs from one place to another. Also, low wettability of the substrate to the liquid agent causes the substrate to repel the liquid agent even when they come into contact with each other. In this case, the liquid agent around the repelled portion sometimes surrounds this repelled portion and forms a bubble.
Furthermore, in this method a liquid agent vessel cannot be easily kept clean and requires a long cleaning time.
A resist which has become soluble dissolves in the development step. This resist sometimes comes in contact with the wall of the vessel and becomes particles. Additionally, the developer is an alkaline aqueous solution. Hence, an alkali component crystallizes by water evaporation or reacts with atmospheric carbon dioxide gas and then a carbonate precipitates. These crystal and carbonate are also the causes of particles and eventually produce defects. Accordingly, it is important to prevent adhesion of these substances and make cleaning easy. A developer reservoir as disclosed in Jpn. Pat. Appln. KOKAI Publication No. 2-101467 has recesses, projections, valves, and the like for supplying and discharging a developer and rinse solution, i.e., has many members difficult to clean. These members cannot be easily kept clean and require a long cleaning time.
The present invention has been made in consideration of the above situation, and has as its object to provide a substrate processing method of supplying a liquid agent so as to perform liquid agent processing with a small consumption amount and bring a liquid agent film into contact with the surface of a substrate to be processed without holding air, and a substrate processing apparatus for carrying out this method.
To achieve the above object, a substrate processing method according to the first aspect of the present invention comprises the steps of
supplying a liquid agent onto a plate-like liquid agent holder to form a liquid agent film on the liquid agent holder,
setting a substrate to be processed such that a surface to be processed of the substrate opposes the liquid agent film on the liquid agent holder,
bringing the surface to be processed of the substrate into contact with the liquid agent film at one point, and
gradually spreading the contact from the one point as a starting point until the surface to be processed of the substrate entirely comes in contact with the liquid agent film.
A substrate processing apparatus according to the second aspect of the present invention comprises
a plate-like liquid agent holder,
a liquid agent supply mechanism configured to supply a liquid agent onto the liquid agent holder to form a liquid agent film on the liquid agent holder,
a holding mechanism configured to hold a substrate to be processed such that a surface to be processed of the substrate opposes the liquid agent holder,
a first driving mechanism configured to move at least one of the liquid agent holder and the substrate to bring an end portion of the surface to be processed of the substrate into contact with the liquid agent film, and
a second driving mechanism configured to move the substrate so as to gradually spread the contact from the end portion of the surface to be processed as a starting point, until the surface to be processed of the substrate entirely comes in contact with the liquid agent film.
A substrate processing apparatus according to the third aspect of the present invention comprises
a plate-like liquid agent holder,
a liquid agent supply mechanism configured to supply a liquid agent onto the liquid agent holder to form a liquid agent film on the liquid agent holder,
a holding mechanism configured to hold a substrate to be processed such that a surface to be processed of the substrate opposes the liquid agent film on the liquid agent holder,
a first driving mechanism configured to curve the surface to be processed of the substrate into a shape of a projection and bringing an end portion of the projection of the surface to be processed into contact with the liquid agent film by moving at least one of the liquid agent holder and the substrate, and
a second driving mechanism configured to cancel the curve of the substrate so as to gradually spread the contact from the end portion of the projection of the surface to be processed as a starting point, until the surface to be processed of the substrate entirely comes in contact with the liquid agent film.
In the present invention, after a thin liquid agent film is formed by supplying a liquid agent onto a plate-like developer holder, this liquid agent film and the surface to be processed of a substrate to be processed are opposed. A portion of the liquid agent film and a portion of the substrate are brought into contact with each other by declining the substrate and moving it close to the liquid agent film and making the projection close to the liquid agent film, or by curving the substrate toward the liquid agent film. After that, the surface to be processed of the substrate is made parallel to the liquid agent film, and the liquid agent is supplied such that the contact area of the liquid agent film spreads on the entire surface to be processed by the interfacial tension between the liquid agent film and the surface to be processed. Since a thin liquid agent film can be uniformly formed below the substrate, liquid agent processing can be performed with a small consumption amount. Additionally, the liquid agent can be supplied to the substrate without holding air.
To effectively supply the liquid agent without bubbles or processing variation to the substrate to be processed, it is desirable that the contact angle between the surface to be processed and the liquid agent is 40xc2x0 or less. This contact angle of 40xc2x0 is achieved by adding a surfactant to the liquid agent or by performing surface treatment on the surface to be processed before processing.
Also, to allow the liquid agent to spread easily on the liquid agent holder, it is desirable to select the materials and the like of the liquid agent and the liquid agent holder such that the contact angle between the liquid agent holder and the liquid agent is 30xc2x0 or less. When the materials and the like are thus selected, it is possible to decrease the thickness of the liquid film, achieve uniform development, and reduce the liquid agent amount.
The above contact angle can be calculated as follows. The liquid agent is dropped onto the surface to be processed or onto the liquid agent holder such that the diameter of the droplet is 2 mm or less. FIG. 15 shows the section of this droplet. Referring to FIG. 15, xcex8 is the contact angle. This contact angle xcex8 is the angle between the substrate surface and the tangent of the droplet at the portion where the outside circle of the droplet 401 crosses the surface of a substrate 400 to be processed. Assuming the outside circle of the droplet is part of a circle, this contact angle is approximated by
xcex8=2xcex81=2 tanxe2x88x921(h/r) 
where h is the height of the droplet, and r is xc2xd the base of the droplet.
In the present invention, development is performed by supplying the liquid agent film onto the plate-like liquid agent holder. Therefore, necessary amount of liquid agent in this invention is less than the one in the case of dipping. Also, since the liquid agent holder is a plate, the holder surface has neither projections nor recesses, and this permits easy removal of particles by cleaning. Consequently, the liquid agent holder can be kept clean.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.